The present disclosure relates to semiconductor processing methods, and particularly to a lithographic material stack including a metal-compound hard mask layer and a method for forming the same.
Titanium nitride (TiN) is a material that provides high etch selectivity to organic materials such as photoresist materials and organic planarization materials, and dielectric materials such as SiN, SiO2 and low-k dielectric materials. Thus, organic materials and dielectric materials can be etched selective to TiN. However, TiN has a high extinction coefficient k value and is not an anti-reflective material. The value of the extinction coefficient k of TiN is in a range from 0.9 to 3.8 in the visible wavelength range. The high extinction coefficient of TiN poses a significant problem for the purpose of overlay alignment. In a lithographic stack in which a TiN layer is employed as a hard mask layer, if the TiN layer is too thick, an overly signal for the purpose of alignment from underlying lithographic alignment material layers is too weak, and lithographic alignment cannot be performed reliably. If the TiN layer in a lithographic stack is too thin, the fidelity of the image memorized into the TiN layer for the purpose of dual image transfer is degraded, and the shape of the pattern memorized in the TiN layer may be distorted.